Re: [RFC][PATCH 3/3] x86: Add workaround to NMI iret woes

[Peter Zijlstra]

On Fri, 2011-12-09 at 10:00 -0500, Steven Rostedt wrote:
> On Fri, 2011-12-09 at 10:22 +0100, Peter Zijlstra wrote:
> 
> > Its was definitely tongue in cheek, also I did say this'll be a massive
> > pain with paravirt since I doubt paravirt calls are NMI safe. 
> 
> But does paravirt simulate NMIs? Does a guest ever take an NMI? I can
> enable paravirt to see if it breaks. 

KVM does NMIs, the write_idt thing is a paravirt call. Then again, a
vcpu is a single thread of execution, there can only ever be 1 hypercall
at the same time.

The only thing that remains is if the hypercall interface is NMI-safe,
what if the NMI comes in just as another context is also starting a
hypercall. I really don't know enough about all that crap to know.


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